Vincent Jost

Simultaneous optimization of classical objectives in JIT scheduling

Just-in-time production models have been developed in recent years in order to reduce costs of diversified small-lot productions. The methods aim at maintaining the production rate of each type of part as smooth as possible and therefore holding small inventory and shortage costs. Different ways of measuring the slack between a given schedule and the ideal no-inventory no-shortage production have been considered in the literature. This paper compares the three most studied objective functions and refutes several conjectures that have been formulated in the last few years.

Call-Based Dynamic Programming for the Precedence Constrained Line Traveling Salesman

The Precedence Constrained Line Traveling Salesman is a variant of the Traveling Salesman Problem, where the cities to be visited lie on a line, the distance between two cities is the absolute difference between their abscissae and a partial ordering is given on the set of cities. Such a problem is encountered on linear construction schemes for instance. Using key dominance properties and lower bounds, we design a call-based dynamic program able to solve instances with up to 450 cities.

Note: Small deviations, JIT sequencing and symmetric case of Fraenkel's conjecture

We prove Fraenkels conjecture for the special case of symmetric words, and show that this proof implies the conjecture of Brauner and Crama [Facts and questions about the maximum deviation just-in-time scheduling problem, Discrete Appl. Math. 134 (2004) 25-50] concerning instances of the just-in-time sequencing problem with maximum deviation B^*<12.

Trains do not vanish: the ROADEF/EURO challenge 2014

The ROADEF/EURO challenge is a contest jointly organized by the French Operational Research and Decision Aid society (ROADEF) and the European Operational Research society (EURO). The contest has appeared on a regular basis since 1999 and always concerns an applied optimization problem proposed by an industrial partner. The 2014 edition of the ROADEF/EURO challenge was led by the Innovation & Research department of SNCF, a global leader in passenger and freight transport services, and infrastructure manager of the French railway network. The objective of the challenge was to find the best way to store and move trains on large railway sites, between their arrivals and departures. Since trains never vanish and traffic continues to increase, in recent years some stations have been having real congestion issues. Train management in large railway sites is of high interest for SNCF, which is why it was submitted to the operations research community as the industrial problem for the 2014 edition of the ROADEF/EURO challenge. This paper introduces the special section of the Annals of Operations Research volume devoted to the ROADEF/EURO challenge 2014, as well as the methods of the finalist teams and their results.